This proposal outlines research whose long-term objective is to provide a rational basis for the design of novel approaches to neurological rehabilitation, by gaining insight into the relevant mechanisms of neural plasticity. The proposal focuses on adult neural plasticity as manifested in perceptual learning, which is the progressive improvement in performance with practice of previously unfamiliar perceptual tasks. Perceptual learning will be explored in the domain of tactile texture perception, by stroking gratings consisting of alternating ridges and grooves across the fingerpad. Specific Aim 1, the psychophysical characterization of perceptual learning in normal humans, consists of the following component aims: (A) to define the learning curve along which texture (grating) discrimination thresholds decrease on a given finger, with training; (B) to assess the site-specificity of learning effects in tactile texture discrimination, by comparing posttraining performance on the trained finger (1.A) with that on other, untrained fingers; (C) to assess the task-specificity of learning effects, by examining the transferability of improved discrimination on one set of gratings differing only in groove width to another set differing only in ridge width; (D) to clarify the role of focussing attention spatially and on task- specific attributes, by comparing performance improvement in grading discrimination on a given finger in 1.A to that after exposure to a similar range of gratings on the same finger but with attention directed to: (a) another task, discriminating variations in contact force, on the same finger; or (b) discriminating gratings presented simultaneously to another finger. Specific Aim II is the neurophysiological elucidation of the cortical basis of perceptual learning. To this end, single-neuron responses will be recorded in primary somatosensory cortex of trained monkeys during grating discrimination. Neuronal responses will be compared at different points in time to identify neural mechanisms underlying improvement in grating discrimination on specific fingers (as in 1.B0 and on specific grating sets (as in 1.C). Specific Aim III is the application of perceptual training in a neuro- rehabilitative setting. Patients with strokes resulting in impaired grating discrimination will be trained intensively on grating discrimination, in an effort to maximize improvement in their deficits.